Sheet materials having physical characteristics which allow for air permeability and moisture vapor permeability are well known and are generally referred to as porous sheets. Porous sheet materials are typically non-woven, woven or knitted constructions although foamed sheets, microporous films and perforated films also provide certain degrees of permeability.
Porous sheet materials have many applications and are particularly useful as backings for tapes in the medical field. This is particularly true when it is desirable to allow the skin covered by the sheet material to breathe. When an adhesive is coated onto a porous sheet, the adhesive sheet article will exhibit varying degrees of breathability depending upon the nature of both the porous sheet and the adhesive coated thereon. For example, Copeland in U.S. Pat. No. 3,121,021 describes a breathable surgical tape made of a non-woven backing and a microporous layer of pressure-sensitive adhesive.
Certain porous sheets coated with adhesive may permit or even facilitate the migration of adhesives into the porous sheet layer. Such migration of adhesives is not always detrimental to the performance of the adhesive tape article. This is true if a heavy adhesive coating is used or if the adhesive is used for transdermal delivery of a bioactive molecule. However, it is sometimes detrimental when the adhesive migrates into the porous sheets. This is true when adhesion of the resulting article is reduced due to the migrated adhesive.
When it is necessary to control or limit the migration of adhesive, a few strategies are available. Generally, one should avoid "soft" adhesives which readily migrate into the interstices of porous backings. "Soft" adhesives include adhesives such as acrylate ester-acrylic acid-polyethylene oxide acrylate macromer copolymers which provide adhesive coated sheet materials having a skin adhesion value of at least about 2.2 Newtons per 100 millimeters of width. However, such "soft" adhesives are very desirable for adhering to skin because "soft" adhesives are generally very conformable and usually adhere well to skin, and may adhere to moist skin.
U.S. Pat. No. 5,344,415 of DeBusk and Felice (hereinafter "DeBusk") describes a multi-component system which includes a web and adhesive layer, a barrier layer and a second adhesive layer. The DeBusk barrier layer is a distinct and separate transparent nonexclusive film material such as a polyurethane film. As is generally known in the art, films must be at least 25 micrometers thick in order to allow handling of the film. The DeBusk barrier layer (film) is sandwiched between 2 layers of adhesive and does not directly contact the web. DeBusk teaches that the barrier layer provides a barrier to external contaminants, restricts drainage strike-through and helps maintain a desirable moist environment.
It is an object of the present invention to provide porous adhesive sheet articles wherein the migration of the soft adhesives into the porous sheeting is limited or prevented.